The invention concerns a device for the angular adjustment of a camshaft relative to the crankshaft of an internal combustion engine, particularly a vane-type adjuster comprising a stator that is driven by the crankshaft preferably through a traction element and a drive pinion, and a vane rotor that is rotationally fixed to the camshaft and possesses a means, preferably an axially displaceable fixing pin for effecting a releasable, rotational fixing of the vane rotor.
A generic device of the pre-cited type is known from DE 196 23 818 A1. In this device, the stator is screwed to a front plate and a chain sprocket which together form a housing with hydraulic chambers in which a vane rotor with vanes sub-dividing the hydraulic chambers is arranged for pivoting. The individual chambers can be pressurized by pressure oil delivered through hydraulic ducts, so that the vane rotor can pivot within a defined angular range or be fixed in any desired intermediate position. If the oil pressure falls below a certain minimum value (at a standstill or starting of the engine, or at a low engine speed), a locking member that is mounted for axial displacement in one of the vanes of the vane rotor, is pushed by spring force into an opening of the front plate. This causes the vane rotor and the stator to be non-rotatably coupled to each other, so that the camshaft is then driven directly by the chain sprocket. In this way, rattling noises are prevented at low engine speeds and an optimal adjustment of the inlet camshaft for starting the engine is assured. With increasing engine speed and a concomitant rise of the oil pressure, the locking of the vane rotor is released so that the angular adjustment function becomes effective again.
A drawback of this device is its lack of oil-tightness so that the device is only suitable for oil-tight encapsulated drives with a chain or gearwheel. For toothed belt drives, that are interesting from the cost and noise point of view, the aforesaid drive does not come into question.
The object of the invention is therefore to provide a device for the angular adjustment of a camshaft that is also suitable for a toothed belt drive and can be economically manufactured.
This invention achieves this object by the fact that all components of the vane-type adjuster that have contact with pressure oil are arranged in an oil-tight housing. These components include at least the stator and the vane rotor and a means for a releasable, rotational fixing. Due to the oil-tight design of the vane-type adjuster, this can be driven by a toothed belt.
The oil-tight housing can be made, for example, as a turned part or by investment casting, injection molding, sinter molding or forging. Particularly economically, it is made as a deep drawn part out of steel sheet. Deep drawing permits the use of an inexpensive base material that can be given the final shape by a simple shaping method and only a small amount of subsequent machining. Due to the fact that the oil-tight housing comprises a camshaft-proximate housing part and a camshaft-distal housing part having approximately the same depth of deformation, an economic fabrication of the housing is assured.
Advantageously, the housing parts have a flat bottom whose periphery merges into a cylindrical section which continues into an outwardly extending flange. The housing is rendered oil-tight by a sealing of the individual flange connections. It is also conceivable to omit the cylindrical section on one of the housing parts and let its flat bottom merge directly into the radial flange. It is further conceivable to make this flange continue into an outer cylindrical portion having the profile of the toothed belt pulley rolled into its outer peripheral surface. This measure would eliminate the need of a separate toothed belt pulley and its fixing means.
It has proved to be of advantage that the flanges and the drive pinion can be connected to one another by flange screws equally spaced around the periphery of the vane-type adjuster and that the flange screws are configured as fitting screws that can be screwed into threaded bores of the drive pinion. Due to the fact that the flange screws are situated outside the pressure oil region, they cannot cause any oil leakage problems. The configuration of the flange screws as fitting screws assures a reliable transmission of the camshaft torque irrespective of the magnitude of the surface pressure between the flanges.
According to a further advantageous feature of the invention, a flat, appropriately sized compensating washer is arranged between at least one of the flat bottoms and the stator, and the diameter of this washer, with clearance, corresponds to the inner diameter of the cylindrical section. Compensating washers are available in a variety of thicknesses and permit a compensation of manufacturing tolerances of the deep drawn housing parts and their deformation caused by the tightening of the flange screws. This permits the setting of the axial play between the flanges that is needed for producing the bracing between the inner components of the vane-type adjuster required for the transmission of the camshaft torque. The radial and axial play of the vane rotor required for the freedom of movement and sealing of the vane rotor is assured by an appropriate working of the vane rotor and the stator.
The transmission of the camshaft torque is achieved by the fact that the drive pinion, the flanges, the housing parts, the compensating washers and the stator can be braced rotationally fast to one another with the help of the flange screws. An advantage of this is that the biasing force of the flange screws acts, above all, in the peripheral region of the friction members and therefore at the largest friction radius. The resulting friction forces are augmented by the fact that the braced surfaces, especially the side surfaces of the stator are profiled. In this way, the friction engagement is enhanced by additional positive engagement.
Another advantageous feature of the invention is that the compensating washer that is arranged on the side of the vane rotor from which the fixing pin extends, has a locking bore into which the fixing pin can snap. By reason of the locking bore, the compensating washer is at the same time a locking disc. The locking bore in the form of a through-bore is simple to make. The flat bottom serves as a stop for the fixing pin.
Due to the fact that an O-ring seal is arranged in a groove between the inner surfaces of the cylindrical sections and the flanges that is formed by the transition radius resulting from the manufacturing process, a groove that already exists is utilized for sealing the flanges.
To summarize, it will be appreciated that, due to the oil-tight encapsulation of all the components that are pressurized by the pressure oil, the vane-type adjuster of the invention permits the use of an economic and low-noise toothed belt drive for the camshaft. The use of deep drawn components for the oil-tight housing offers additional cost advantages.
Further features of the invention will become obvious from the following description of the drawings and from the drawings themselves which give a schematic representation of one example of embodiment of the invention.